Abstract

Ontogenic studies of human prosociality generally agree on that human prosociality increases from early childhood through early adulthood; however, it has not been established if prosociality increases beyond early adulthood. We examined a sample of 408 non-student residents from Tokyo, Japan, who were evenly distributed across age (20-59) and sex. Participants played five economic games each separated by a few months. We demonstrated that prosocial behavior increased with age beyond early adulthood and this effect was shown across all five economic games. A similar, but weaker, age-related trend was found in one of three social value orientation measures of prosocial preferences. We measured participants' belief that manipulating others is a wise strategy for social success, and found that this belief declined with age. Participants' satisfaction with the unilateral exploitation outcome of the prisoner's dilemma games also declined with age. These two factors-satisfaction with the DC outcome in the prisoner's dilemma games and belief in manipulation-mediated the age effect on both attitudinal and behavioral prosociality. Participants' age-related socio-demographic traits such as marriage, having children, and owning a house weakly mediated the age effect on prosociality through their relationships with satisfaction with the DC outcome and belief in manipulation.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1. Relationships of age with overall…

Fig 1. Relationships of age with overall prosocial behavior.

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Each gray circle corresponds to an…

Fig 1. Relationships of age with overall prosocial behavior.

Each gray circle corresponds to an individual participant’s prosocial behavior, and each red circle represents the 5-year mean. The size of each gray circle indicates the number of the same age participants who had the same prosocial behavior score, and each red circle indicates the sample size for each 5-year age range. Error bars represent standard errors.

Fig 2. Relationships between age and prosocial…

Fig 2. Relationships between age and prosocial behavior.

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The positive relationship between age and prosocial…

Fig 2. Relationships between age and prosocial behavior.

The positive relationship between age and prosocial behavior (blue line) is maintained after controlling for SVO prosociality (adjusted for SVO, green line) or satisfaction with the DC outcome (adjusted satisfaction, red line). The relationship ceases to be significant when the satisfaction of the DC outcome and the belief in manipulation are controlled (adjusted satisfaction and belief, black line).

Fig 3. Regression lines each representing the…

Fig 3. Regression lines each representing the effect of age on prosocial behavior for a…

Fig 3. Regression lines each representing the effect of age on prosocial behavior for a level of the three SVO measures, and satisfaction with the DC outcome.

These lines represent regression lines obtained from the regression equations including both the main and the interaction effects. The SLM was dichotomized to proselfs and prosocials in this figure, and so are satisfaction (below or above the scale mid-point of 4).

Fig 4. The relationship between satisfaction with…

Fig 4. The relationship between satisfaction with the four PDG cells and age (in 10-year…

Fig 4. The relationship between satisfaction with the four PDG cells and age (in 10-year intervals).

Fig 4 shows the levels of happiness vs. unpleasant for the CC outcome (blue line), for the DC outcome (red line), for the CD outcome (green line), and for the DD outcome (orange line). Transformers refer to the proportion of the participants who have subjectively transformed the PDG to a coordination game. Error bars represent standard errors.

Grant support

23223003 and 15H05730, Japan Society for the Promotion of Science, https://www.jsps.go.jp/. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.